Often, electrical amplifiers have a two-stage construction. In a first stage, an intermediate circuit generator or a power supply unit generates a supply voltage of medium amplitude or precision. The supply voltage and intermediate circuit generator supply an output stage for generating an output signal with the desired properties. Depending on requirements, the output signal may have a voltage that is transformed upward compared to the supply voltage and, may have predeterminable constant or time-dependent signal properties. For use as a gradient amplifier for gradient coils in magnetic resonance systems, especially fast-time dependent output signal properties that must be adhered to precisely must be assured.
The precision with which the desired parameter values of the output signal, such as current or voltage, can be adhered to depends, among other factors, on fluctuations in the power supply voltage. Under some circumstances, fluctuations in the power supply voltage can be partly compensated for by circuitry of the output stage. However, complete compensation is not always possible, and hence not all the requirements made of the output signal can readily be met.
With a view to the quality of the output signal, a stabilized power supply unit is employed. In addition, the desired parameters of the output signal can be regulated, and the regulator, for instance, regulates switching times of switch elements of the output stage. Such regulation can be adapted optimally to the desired mode of operation of the output stage, so as to minimize the effects of a fluctuating supply voltage. Nevertheless, at critical operating points, for instance when the time-dependent properties of the output signal are changing rapidly, an influence of the power supply signal remains. Depending on the output signal requirements, additional compensation for supply fluctuations can therefore be desirable.